1. Field of the Invention
The present invention relates to a zinc oxide-based sputtering target.
2. Description of the Related Art
As a transparent conductive film for use in, for example, electronic devices, indium tin oxide (ITO) and the like have been widely used for many years. However, due to price increase of rare metals such as indium, rare-metal alternatives are strongly desired. Accordingly, attempts have been actively made in recent years to use less expensive zinc oxide (ZnO) for producing transparent conductive films, but ZnO is not yet extensively used because there are various problems, for example, the resistance is not sufficiently lowered, and a desired electrical conductivity cannot be obtained. Therefore, a zinc oxide film with higher transparency and electrical conductivity is desired as a transparent conductive material that substitutes for ITO.
It is also known that a highly uniform film can be obtained by sputtering with a sputtering target composed of (002) plane-oriented zinc oxide. For example, Patent Document 1 (JP 33017558) discloses an electrically conductive zinc oxide sintered body having an average sintered grain diameter of 1 μm to 10 μm, a volume resistivity of less than 10 Ω·cm, a density of 4.0 g/cm3 or greater and less than 5.0 g/cm3, and (002) crystal orientation greater than (101) crystal orientation. Patent Document 2 (JP H6-88218A) discloses a zinc oxide-based sintered body having (002) crystal orientation greater than (101) crystal orientation and a density of 4.5 g/cm3 or greater. However, the object of Patent Documents 1 and 2 is to form a low-resistance film or to form a film with a small resistance distribution on a low-temperature substrate, and the resistivity at ordinary substrate temperatures and the transmittance in a near-infrared region of the film are inadequate.
Patent Document 3 (JP 3864425B) discloses a high-density ZnO-based sputtering target in which the maximum diameter of aggregates of the dispersed aluminum component is controlled in order to stably form a film having lower resistance. However, Patent Document 3 is silent on the spinel phase distribution and its influence on the resistivity and the transmittance in a near-infrared region of the film.
Patent Document 4 (JP 2006-200016A), Patent Document 5 (JP 2010-70448A), Patent Document 6 (JP 2010-111560A), and Patent Document 7 (JP 2013-112833A) disclose a ZnO-based sputtering target in which the grain diameter or the distribution of the Al-containing phase is controlled, in order to suppress arcing or improve the moisture resistance of the film. However, the resistivity and the light transmittance in a near-infrared region of the film are inadequate.
Patent Document 8 (JP 2011-63866A) discloses a ZnO-based sputtering target for a film having improved light transmittance in an infrared region and heat resistance by adding Al and Mg and controlling the grain diameter of the Al-containing spinel phase. The grain diameter of the spinel phase is controlled in order to suppress arcing, and the influence on the resistivity and the light transmittance in a near-infrared region of the film is not described.